Light-emitting device

ABSTRACT

This disclosure discloses a light-emitting device. The light-emitting device comprises: a substrate; and a first light-emitting unit comprising a plurality of light-emitting diodes electrically connected to each other on the substrate. A first light-emitting diode in the first light-emitting unit comprises a first semiconductor layer with a first conductivity-type, a second semiconductor layer with a second conductivity-type, and a light-emitting stack formed between the first and second semiconductor layers. The first light-emitting diode in the first light-emitting unit further comprises a first connecting layer on the first semiconductor layer for electrically connecting to a second light-emitting diode in the first light-emitting unit; a second connecting layer, separated from the first connecting layer, formed on the first semiconductor layer; and a third connecting layer on the second semiconductor layer for electrically connecting to a third light-emitting diode in the first light-emitting unit.

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/437,908, entitled “Light-emitting device”, filed on May 8,2009, and the content of which is hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a light-emitting device, and inparticular to a light-emitting device comprising a plurality of recessesin a semiconductor window layer.

2. Description of the Related Art

The light-emitting diodes (LEDs) of the solid-state lighting elementshave the characteristics of the low power consumption, low heatgeneration, long operational life, shockproof, small volume, quickresponse and good opto-electrical property like light emission with astable wavelength, so the LEDs have been widely used in householdappliances, indicator light of instruments, and opto-electricalproducts, etc. However, how to improve the light-emitting efficiency oflight-emitting devices is still an important issue in this art.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a light-emitting device.

The light-emitting device comprises: a substrate; a transparentconductive layer disposed on the substrate; a semiconductor window layerformed on the transparent conductive layer and having a flat surface anda plurality of recesses, wherein each of the recesses has a side wallsurface; and a light-emitting stack formed on the semiconductor windowlayer and comprising a first conductivity semiconductor layer, a secondconductivity semiconductor layer, and an active layer sandwiched betweenthe first and second conductivity layers. The side wall surface of oneof the recesses is inclined with respect to the flat surface, and thecontact resistance between the flat surface and the transparentconductive layer is less than that between the side wall surface in eachrecess and the transparent conductive layer.

In another embodiment of the present disclosure, a light light-emittingdevice is provided.

The light light-emitting device comprises: a substrate; a transparentconductive layer disposed on the substrate; a semiconductor window layerformed on the transparent conductive layer and having a flat surface anda plurality of recesses, wherein each of the recesses has a side wallsurface; an ohmic contact layer formed between the semiconductor windowlayer and the transparent conductive layer; and a light-emitting stackformed on the semiconductor window layer and comprising a firstconductivity semiconductor layer, a second conductivity semiconductorlayer, and an active layer sandwiched between the first and secondconductivity layers. The semiconductor window layer and the ohmiccontact layer comprise the same material.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide easy understanding ofthe application, and are incorporated herein and constitute a part ofthis specification. The drawings illustrate the embodiments of theapplication and, together with the description, serve to illustrate theprinciples of the application.

FIG. 1 shows a cross-sectional view of a light-emitting device inaccordance with the first embodiment of the present disclosure.

FIG. 2 shows a cress-sectional view of a light-emitting device inaccordance with the second embodiment of the present disclosure.

FIG. 3 shows a cross-sectional view of a light-emitting device inaccordance with the third embodiment of the present disclosure.

FIGS. 4A to 4C show plan views of recesses in accordance with thepresent disclosure.

FIGS. 5A to 5G are cross-sectional views showing a method of making thelight-emitting device of the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For to better and concisely explain the disclosure, the same name or thesame reference number given or appeared in different paragraphs orfigures along the specification should has the same or equivalentmeanings while it is once defined anywhere of the disclosure.

The following shows the description of the embodiments of the presentdisclosure in accordance with the drawings.

FIG. 1 discloses a light-emitting device 100 according to the firstembodiment of the present disclosure. The light-emitting device 100comprises a permanent substrate 10, a bonding layer 18, a reflectivelayer 11, a transparent conductive layer 12, an ohmic contact layer 13,a semiconductor window layer 14, and a light-emitting stack 15. Thelight-emitting stack 15 comprises a p-type semiconductor layer 151, ann-type semiconductor layer 153, and an active layer 152 sandwichedbetween the p-type and n-type semiconductor layers 151, 153. Thesemiconductor window layer 14 has a flat surface 141 and a plurality ofrecesses 142. Each of the recesses has a side wall surface 1421 which isinclined with respect to the flat surface 141 at an angle (Θ) greaterthan 90° and less than 180°. Preferably, the angle (Θ) ranges from 110°to 160°. In this embodiment, the recesses 142 have triangular shapedcross-sections. The ohmic contact layer 13 is formed between thesemiconductor window layer 14 and the transparent conductive layer 12 atposition corresponding to the flat surface 141 of the semiconductorwindow layer 14. A surface area ratio of the surface area of the ohmiccontact layer 13 to the surface area of the semiconductor window layer14 ranges from 10% to 90%. The recesses have a depth (H) and the depthratio of the depth of the recesses 142 to the thickness of thesemiconductor window layer 14 ranges from 20% to 80%.

Referring to FIG. 1, the light-emitting device 100 further comprises ann-side electrode 16 formed on the light-emitting stack 15 and a p-sideelectrode 17 formed on the permanent substrate 10. The n-side electrode16 comprising a bonding pad 160 and an extension 161 extending from thebonding bad 160 are formed on the light-emitting stack 15 at positionscorresponding to the recesses 142. In this embodiment, the ohmic contactlayer 13 is substantially made of the same material as the semiconductorwindow layer 14. In addition, the ohmic contact layer 13 furthercomprises doping impurities for ohmically contacting the transparentconductive layer 12. Therefore, the contact resistance between the flatsurface 141 and the transparent conductive layer 12 is less than thatbetween the side wall surface 1421 and the transparent conductive layer12, which results in that, when a power source is applied on the n-sideelectrode 16, most current flows through the flat surface 141 of thesemiconductor window layer 14, thereby obtaining a current-blockingeffect between the side wall surface 1421 and the transparent conductivelayer 12. Furthermore, the light emitted from the light-emitting stack15 is reflected at the side wall surface 1421 and is directed to escapefrom a light-emitting surface of the light-emitting stack 15 forenhancing the light extraction efficiency. The semiconductor windowlayer 14 is made of a material selected from the group consisting ofGaP, InGaP, GaAs, AlGaAs, and combinations thereof. The dopingimpurities comprise a material selected from the group consisting of Mg,Be, Zn, C, and combinations thereof.

FIG. 2 discloses a light-emitting device 200 according to the secondembodiment of the present disclosure. The second embodiment of thelight-emitting device 200 has the similar structure with the firstembodiment of the light-emitting device 100 except that the recesses 142have trapezoid shaped cross-sections and each of the recesses 142further has a recessed surface 1422. The recessed surface 1422 in eachrecess 142 is substantially parallel to the flat surface 141. Thebonding pad 160′ and the extension 161′ are formed at positionscorresponding to the recessed surface 1422 and the side wall surface1421. Alternatively, the n-type electrode 16 can be merely formed atposition corresponding to the recessed surface 1422 (not shown). Thecontact resistance between the recessed surface 1422 and the transparentconductive layer 12 is substantially equal to that between the side wallsurface 1421 and the transparent conductive layer 12. It is noted thatthe cross-section of the recesses 142 comprises at least one patternselected from the group consisting of triangular shape, trapezoid shape,and combinations thereof.

FIG. 3 shows a light-emitting device 300 according to the thirdembodiment of the present disclosure. The third embodiment of thelight-emitting device 300 has the similar structure with the firstembodiment of the light-emitting device 100 except that the side wallsurface 1421 of some of the recesses 142 is not inclined to the flatsurface 141. In this embodiment, the recess 142 formed beneath thebonding pad 160″ has the side wall surface 1421 substantiallyperpendicular to the flat surface 141, and the recess 142 formed beneaththe extension 161″ has the side wall surface 1421 inclined to the flatsurface 141.

FIGS. 4A and 4B are plan views of the n-type electrode 16 and therecesses 142. The recesses 142 as shown in FIG. 4B have a first patternwhich is geometrically similar to that of the n-type electrode 16 asshown in FIG. 4A and are formed beneath the n-type electrode 16. FIG. 4Cis a plan view of the recesses 142 which further have a second pattern.The second pattern is a tessellation of hexagons which are not formedbeneath the n-type electrode 16. Alternatively, in a plan view, thesecond pattern can be a circle, or a tessellation of triangle,rectangle, or pentagon. Depending on the actual requirements, thepattern of the n-side electrode 16 may vary and therefore the firstpattern of the recesses 142 will vary with the pattern of the n-sideelectrode 16.

FIGS. 5A to 5G illustrate a method of making the light-emitting device200 according to the second embodiment of the present disclosure.Referring to FIG. 5A, the n-type semiconductor layer 153, the activelayer 152, the p-type semiconductor layer 151, and the semiconductorwindow layer 14 are sequentially grown on a growth substrate 20.Referring to FIG. 5B, the ohmic contact layer 13 is grown on thesemiconductor window layer 14. The semiconductor window layer 14 has athickness ranging from 1 μm to 10 μm and the ohmic contact layer 13 hasa thickness less than 2000 Å. Alternatively, the semiconductor windowlayer 14 can be subjected to a doping treatment to form the ohmiccontact layer 13. Referring to FIG. 5C, an etching process is carriedout to remove portions of the ohmic contact layer 13 and further toremove portions of the semiconductor window layer 14 such that therecesses 142 are formed within the semiconductor window layer 14.Referring to FIG. 5D, the transparent conductive layer 12 is formed onand conformal to the ohmic contact layer 13 and the semiconductor windowlayer 14 by evaporating or sputtering. Therefore, the transparentconductive layer 12 is in contact with the semiconductor window layer 14and the ohmic contact layer 13. It is noted that when the transparentconductive layer 12 is formed by spin coating, the recesses 142 isfilled up with the transparent conductive layer 12. Referring to FIG.5E, the reflective layer 11 is formed on the transparent conductivelayer 12. Referring to FIG. 5F, the permanent substrate 10 is bonded tothe reflective layer 11 through the bonding layer 18. Referring to FIG.5G, the growth substrate 20 is separated from the n-type semiconductorlayer 153 by etching. Subsequently, the n-side electrode 16 and thep-side electrode 17 are respectively formed on the n-type semiconductorlayer 153 and the permanent substrate 10. The bonding layer 18 comprisesmetal or glue. The metal comprises gold (Au), indium (In), tin (Sn), andcombinations thereof. The glue is made of a material selected from thegroup consisting of indium tin oxide (ITO), benzocyclobutene (BCB),epoxy resin (Epoxy), polydimethylsiloxane (PDMS), silicone (SiOx),aluminum oxide (Al₂O₃), titanium dioxide (TiO2), silicon nitride (SiNx),and combinations thereof.

EXAMPLES Example 1 (E1)

The light-emitting device has a structure as shown in FIG. 2. The n-typesemiconductor layer 153 of AlInP, the active layer 152 of AlGaInP, andthe p-type semiconductor layer 154 of AlInP are sequentially grown onthe growth substrate 20 of GaAs. The semiconductor window layer 14 madeof GaP and having a thickness of 10 μm is grown on the p-typesemiconductor layer 154. The ohmic contact layer 13 made of carbon-dopedGaP is grown on the semiconductor window layer 14 by metal organicchemical vapor deposition (MOCVD). A wet etching is performed to etchportions of the ohmic contact layer 13 and the semiconductor windowlayer 14, thereby forming the recesses 142. The recesses 142 have adepth (H) of about 2 μm, and the depth ratio of the depth of therecesses 142 to the thickness of the semiconductor window layer 14 isabout 20%. The transparent conductive layer 12 made of ITO is formed onthe semiconductor window layer 14 by evaporating. The reflective layer11 is a multi-layer structure of Ag/Ti/Pt/Au is formed on thetransparent conductive layer 12. The permanent substrate made of Si isbonded to the reflective layer 11 by metal bonding process, and then theGaAs substrate 20 is removed. Subsequently, the n-type electrode 16 isformed on the n-type semiconductor layer 153 at position correspondingto the recesses 142 and has a pattern substantially equal to the firstpattern of the recesses 142 (see FIG. 4A). The surface area ratio of thesurface area of the ohmic contact layer 13 to the surface area of thesemiconductor window layer 14 is about 85%, that is, the surface area ofthe recesses 142 is about 15% of the total area of the semiconductorwindow layer 14.

Example 2 (E2)

The light-emitting device of Example 2 has a similar structure with thatof Example 1, except that the recesses 142 further have the secondpattern of hexagon on which the n-type electrode 16 are not formed (seeFIG. 4C). Accordingly, the surface area ratio of the surface area of theohmic contact layer 13 to the surface area of the semiconductor windowlayer 14 is about 80%, that is, the surface area of the recesses 142 isabout 20% of the total area of the semiconductor window layer 14.

Example 3 (E3)

The light-emitting device of Example 3 has a similar structure with thatof Example 1, except that the thickness of the semiconductor windowlayer 14 is 1 μm. The recesses 142 have a depth (H) of about 0.8 μm, andthe depth ratio of the depth of the recesses 142 to the thickness of thesemiconductor window layer 14 is about 80%.

Example 4 (E4)

The light-emitting device of Example 4 has a similar structure with thatof Example 2, except that the thickness of the semiconductor windowlayer 14 is 1 μm.

Comparative Example 1 (CE1)

The light-emitting device of Comparative Example 1 has a similarstructure with that of Example 1, except that the ohmic contact layer 13and the semiconductor window layer 14 are not etched. Therefore, therecesses 142 are not formed in the semiconductor window layer 14.

Comparative Example 1 (CE2)

The light-emitting device of Comparative Example 2 has a similarstructure with that of Example 3, except that the ohmic contact layer 13and the semiconductor window layer 14 are not etched. Therefore, therecesses 142 are not formed in the semiconductor window layer 14.

TABLE 1 Luminous Improved intensity (mcd) percentage E1 469.18 118% E2493.68 124.1%   CE1 397.77 100%

TABLE 2 Luminous Improved intensity (mcd) percentage E3 396.08 112.5% E4459.21 130.4% CE2 352.19   100%

Tables 1 and 2 show experimental results. Compared to the ComparativeExample 1, the light-emitting device of Example 1 has the luminousintensity of 469.18 mcd, which is increased by 18%, and thelight-emitting device of Example 2 has the luminous intensity of 493.68mcd, which is increased by 24.1%. Likewise, compared to the ComparativeExample 2, the light-emitting device of Example 3 has the luminousintensity of 369.08 mcd, which is increased by 12.5%, and thelight-emitting device of Example 4 has the luminous intensity of 459.21mcd, which is increased by 30.4%. By forming the recesses 142 with theside wall surface 1422 that is inclined, light emitting from thelight-emitting stack 15 is efficiently reflected by the side wallsurface 1422 and is directed to escape from a light-emitting surface ofthe light-emitting stack 15, thereby improving the light emittingintensity. In addition, since the recesses 142 further have the secondpattern, which indicates that the area of the recesses 142 in Examples 2and 4 is higher (about 5%) than that in Examples 1 and 3, there are moreside wall surfaces 1422 for reflecting the light emitting from thelight-emitting stack 15. Therefore, the luminous intensity of thelight-emitting device of Examples 2 and 4 is relatively higher.

It will be apparent to those having ordinary skill in the art thatvarious modifications and variations can be made to the devices inaccordance with the present disclosure without departing from the scopeor spirit of the disclosure. In view of the foregoing, it is intendedthat the present disclosure covers modifications and variations of thisdisclosure provided they fall within the scope of the following claimsand their equivalents.

What is claimed is:
 1. A light-emitting device comprising: a substrate;a transparent conductive layer disposed on the substrate; asemiconductor window layer formed on the transparent conductive layerand having a flat surface and a plurality of recesses, wherein each ofthe recesses having a side wall surface; a light-emitting stack formedon the semiconductor window layer and comprising a first conductivitysemiconductor layer, a second conductivity semiconductor layer, and anactive layer sandwiched between the first and second conductivitysemiconductor layers; and an ohmic contact layer formed on the flatsurface of the semiconductor window layer for ohmically contacting withthe transparent conductive layer, wherein the side wall surface of oneof the recesses is inclined with respect to the flat surface, and thecontact resistance between the flat surface and the transparentconductive layer is less than that between the side wall surface and thetransparent conductive layer, and wherein a surface area ratio of thesurface area of the ohmic contact layer to the surface area of thesemiconductor window layer ranges from 10% to 90%.
 2. The light-emittingdevice of claim 1, wherein the semiconductor window layer and the ohmiccontact layer comprises the same material.
 3. The light-emitting deviceof claim 2, wherein the material is selected from the group consistingof GaP, InGaP, GaAs, AlGaAs, and combinations thereof.
 4. Thelight-emitting device of claim 1, wherein the ohmic contact layer is animpurity-doped semiconductor layer.
 5. The light-emitting device ofclaim 4, wherein the impurity comprise a material selected from thegroup consisting of Mg, Be, Zn, C, and combination thereof.
 6. Thelight-emitting device of claim 1, further comprising an electrode formedon the light-emitting stack at position corresponding to the recesses ofthe semiconductor window layer.
 7. The light-emitting device of claim 6,wherein each of the recesses further has a recessed surface, the contactresistance between the recessed surface and the transparent conductivelayer is substantially equal to that between the side wall surface andthe transparent conductive layer.
 8. The light-emitting device of claim6, wherein the electrode has a pattern, and the recesses has a firstpattern geometrically similar to the pattern of the electrode.
 9. Thelight-emitting device of claim 8, wherein the recesses further have asecond pattern of tessellation.
 10. The light-emitting device of claim1, wherein the ohmic contact layer has a thickness less than 2000 Å. 11.The light-emitting device of claim 1, wherein the semiconductor windowlayer has a thickness ranging from 1 μm to 10 μm.
 12. The light-emittingdevice of claim 11, wherein the recesses have a depth, the depth ratioof the depth of the recesses to the thickness of the semiconductorwindow layer ranges from 20% to 80%.
 13. The light-emitting device ofclaim 1, wherein the side wall surface in each recess is inclined withrespect to the flat surface at an angle greater than 90° and less than180°.
 14. The light-emitting device of claim 1, further comprising areflective layer formed between the transparent conductive layer and thesubstrate.